Constant-clearance piston



May'29, H28. 1,671,310

L. V. FENCE CONSTANT CLEARANCE PI S TON Filed July 19, 1926 m Aafe K Pence- Patented Ma 29, 192s.

unrrao STATES LAFE V. PENCE, OF EL PASO, TEXAS.

CONSTANT-CLEARANCE PISTON.

Application filed July 19, 1926. Serial No. 123,287.

This invention relates to trunk pistons for internal combustion engines.

It is an object of this invention to isolate the skirt portion of a piston from the head so that the major heat transfer to the cylinder walls will be through the, piston rings, permitting the skirt to be made cylindrical and closely fitted to the cylinder bore. In an uninsulated piston, the operating temperatures range from 700 F. at the head to 300 at the skirt with a cylinder wall temperature of 200; about three-eighths of'the heat absorbed by the head reaching the trunk or skirt. In such a piston the major part of the heat flow into-the skirt occurs at the pin bosses so that these bosses, if not relieved, distort the most and are the first to seize or score. It is therefore an object of this invention to. reduce the heat flow to the piston skirt and to cause such flow to enter the skirt walls principally at midsection and at points furthest from the pin bosses, permitting the skirt to float only flexibly connected to the head to allow the trunk to expand uninfiuenced by distortion from the hotter head portion, in order that the skirt clearance can be reduced and the main causes of piston seizure removed.

It is alsoan object of this invention to practically separate the head and skirt portions of a piston by turning the bottom ring groove clear through the back wall and connecting the'two portions by means of slightly flexible cast bars of much less cross section than the normal metal provided back of the rings in usual design. A ring of low heat conductivity such as a 30-40% nickel iron or steel alloy is pressed or cast into the groove back of the ring according to whether the piston is of cast iron or die cast aluminum.

Other and furtherimportant objects of this invention will be apparent from the disclosures in the specification and the accompanyingdrawings. I

This invention (in a preferred form) is illustrated in the drawings and hereinafter more fully described.

On the drawings:

Figure 1 is a side elevation of apiston.

Figure 2 is an enlarged central vertical section taken parallel to the elevation of Figure '1 to show the features ofthis invention.

Figure 3 1s 216886121011 on the line III-III of Figure 2.

As shown on the drawings:

or skirt 10 having piston pin bosses 11 associated therewith, and a piston head 12 having ring grooves 13 for piston rings 14, the head being reinforced by a rib 15 extending parallel to the axis of the pin bosses. In Figure 2, the top 16 of the skirt forms the side wall of the'bottom ring groove, which is cut through to entirely separate the head and skirt, thetwo parts beingtied together by integral bars 17 extending from the head, at points midwayof the axis of the piston pin, tothe central part of the skirt. These struts or bars are made as small as practical to safely carry the maximum inertia loads impressed thereon by'the head, inorder to cutdown the heat transferred therealong. In practice, these bars may have a cross-section of about one-fourth of the normal metal (lOSS-SECtlOIl-01dln 1l]ly-- left back of the bottom ring groove; thus greatly reducing the heat transfer.

A heat insulating ring 18 is split into two parts to be pressed into the bottom ring carbon steel alloy has suitable characteristics. 1

Pure nickel and pure iron each have a thermal conductivity in C. G. S. units of about .14 while 30-40% nickel iron alloy has a much lower conductivity coefiicient, namely about .03. A commercial low carbon steel alloy of this character having about. .29 carbon and 4.20 copper has an even lower coeflicient about .02. It will thus be evident that the use of such an alloy will decrease the heat transfer therethrough to about onefifth of afsolid connection of equivalent area when considering the two contact joints. It is advisable to flatten the ring to produce parallel surfaces free from toolmarks which would later bed in and loosen up the ring.

The combined heat flow through the inserted band and the two cast connections works out at about half the usual amount and with the practically floating cross head trunk or skirt, free from head expansion distortion, will .allow the skirt to be fitted as closely as desired and be perfectly c lindrical giving close oil film contact with t e cylinder at all positions.

The cast bars joining the skirt to the head will be of higher temperature than the skirt and their expansion efl'ect will be slightly more than that of the skirt up to the insulating ring, thus requiring an initial press fit for the ring to counteract this expansion which would otherwise result in gas loadimpacts on the ring if it loosened up.

When the ring is cast into an aluminum piston, in turning the lower ring groove, 8.

,narrow shallow groove can be turned into than necessitated by the prior art.

I claim as my invention: 1. A piston comprising head "and skirt sections cut through the wall and held together by interior tie bars, and a ring of relatively low heat conductivity inserted in said out to reduce the heat transfer from saidhead' to said skirt.

2. A piston comprising head-and skirt portions, ring grooves in the head portion, the lowermost groove extending entirely through the wall of the piston, a ring positioned in said groove within the normal piston ring, said ring having a low coefiicient of heat transfer, and struts tying said head to said skirt.

3; A pistoncomprising head and skirt portions, ring groves in the head portion, the lowermost groove extending entirely through the wall of the piston, a ring positioned in the back part of said groove, said ring being of a40% nickel bearing low carbon steel alloy, and struts-tying said head to said skirt.

4, In a piston, an inserted ring of 30-40% nickel bearing iron alloy separating the head and skirt portions of the piston.

- In testimony whereof I have hereunto subscribed my name. i ,7

- LAFE V. PENCE. 

